Tuesday, 13 January 2015

Making 28 from 2 0 1 5

In Secondary the students are playing a game where they use only the digits 2, 0, 1, and 5, in any order, with the operations +, -, x, ÷ to make numbers.

Like

20 + 15 = 35

or

102 - 5 = 97

Here's a hard challenge.

Can you make the number 28?

You might find that too hard, but I will give you some tips.
When you put an exclamation mark after a number it's called a factorial.

1! = 1
2! = 2 × 1 = 2
3! = 3 × 2 × 1 = 6
4! = 4 × 3 × 2 × 1 = 24

But the strange thing is, 0! = 1

Tip: a zero can be used as a one, like this 0!
The sum to make 28 is 14 + 14 = 28
You can make 14 as 15 - 1.

1 comment:

  1. Justus, I'm really pleased you introduced factorials to us! It obviously inspired Samyak too!

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